Cathode



Oct. 31, 1961 Filed April 29, 1960 L. D. SCHWENDER 3,007,075

CATHODE 2 Sheets-Sheet 1 NV ENTO R Leona/d Z2 Sc/lavender Oct. 31, 19 D.SCHWENDER CATHODE 2 Sheets-Shet 2 Filed April 29, 1960 Uillllfi wareFiled Apr. 29, 1960, Ser. No. 25,601 7 Claims. (Cl. 313-346) Thisinvention relates generally to electron tubes and more specifically toelectron tube cathode electrodes.

It is now recognized that the prior art practice of spraying cathodesleeves with a coating ultimately suitable for electron emission tendsto produce a coating texture which lacks the surface uniformitydesirable in many tube ap plications. It is also recognized that a majorimprovement has been achieved by using a wrap-around coating prepared inthe form of a film which is suitable for cutting into small rectangularpieces and attachment to the cathode sleeve through the use of any oneof a number of labelling techniques such as the technique taught inUnited States patent application Serial Number 453,235, filed in thename of Kerstetter et al. on August 31, 1954 and assigned to the sameassignee as this application. Other labelling techniques may also beused. For example, an adhesive may be applied to either the cathodesleeve or the coating wrap and the cathode sleeve rotated while incontact with the wrap. Also by wetting either the cathode sleeve or thecoating wrap with a suitable solvent, it is possible to bring the wrapclose to the cathode sleeve and use a puff of air to attach the wrap inposition.

Regardless of the labelling technique used, wrapped cathodes at presentinvolve the use of a rectangular shaped piece of coating film which whenwrapped around the cathode sleeve tends to form a vertical seam orundesirable discontinuity in coating uniformity. Tolerances are usuallyestablished which will not allow the seam discontinuity in the form ofan overlap seam. Though under optimum conditions it is best to abutopposite edges of the wrap so as to provide a gapless seam and anabsolute minimum discontinuity, manufacturing tolerances must allow forsome size variation and thus it has been found desirable to set thetolerance range so as to accept a small gap at the seam of the coatingwrap.

In many tube applications it is possible to orient the tes Patent seamof the coating wrap so as to place it immediately opposite a grid siderod or at a position where electron emission density is at a minimum.When so placed, the seam even though of a gap type causes little if anydifficulty. Unfortunately, where automatic machines are used forassembling the tube mount it is sometimes difficult to rotationallypre-orient a cylindrical cathode relative to the grid. Thus it would bedesirable to provide a wrap coated cathode having a seam contour whichminimizes the need for cathode rotational orientation relative to thegrid during tube assembly. It would be desirable further to provide acathode wrap having a seam contour which minimizes differences inpossible electron emission between separate vertical portions of thecathode coating.

Thus it is an object of this invention to minimize orientation problemsbetween the cathode and other electron tube electrodes using awrap-coated cathode.

It is a still further object of this invention to distribute thepossible loss in cathode emission arising from a gap seam in a wrappedcathode over the surface area of the cathode so as to minimize emissionvariations.

Basically, my invention, in at least one aspect, comprises a cathodebase covered with a rhomboidal shaped cathode coating wrap which isapplied to the cathode base material so as to form a spiral seam of nomore than a single turn.

For a better understanding of the present invention, to-

gether with other and further objects and capabilities thereof,reference is made to the following disclosure and appended claims inconnection with the accompanying drawings in which:

FIG. 1 shows a prior art wrapped cathode with vertical seam; and

FIG. 2 shows a top view of a vertical seam wrapped cathode relative to agrid; and

FIG. 3 shows a rhomboidal shaped coating strip about to be applied to acathode base sleeve; and

FIG. 4 shows a spiral wrapped cathode; and

FIG. 5 shows a spiral wrapped cathode positioned within a grid helix.

In FIG. 1 there is shown a prior art cylindrical cathode sleeve 11coated with a vertical seamed electron emissive wrap 15. Basically, theemissive coating wrap 15 may comprise a cast film made from the triplecarbonates, calcium, barium and strontium, in a cellulose binder. Thefilm may be cast on a large smooth casting wheel of the type used infilm fabrication and then stripped when hardened and cut intoindividual'wraps, each wrap being suitable for enclosing one cathode sleeve. For amore detailed teaching, reference is made to the above-mentioned UnitedStates patent application Kerstetter et al.

As shown in FIG. 1, wrap 15, as contemplated by the prior art, is madefrom a rectangularly cut piece of film which when wrapped may form a gap17 between adjacent edges 19. When the cathode sleeve 11 is assembledwith a grid 21, as shown in FIG. 2, gap 17 in the emissive wrap '15 mayappear at a position which affects desirable tube characteristics. Forexample, gap 17 is shown in FIG. 2 closely adjacent the lateral wires ofgrid 21 at a point of desirably high emission density. On the other handif the cathode sleeve were rotated during fabrication so that gap 17were positioned adjacent the side rods, it seems obvious that the lossof emission area would be minimized because gap 17 then would beoriented relative to the grid so as to be in a position from which fewif any electrons are taken. Unfortunately, considerable difficulty andexpense is involved in attempting to orient a cylindrical cathoderelative to the grid where machine assembly is used. Especially is thistrue where the assembly machines in question assemble some tube typesusing prior art sprayed cathodes which do not require pre-orientation.

.In FIG. 3, in accordance with the invention, there is shown a cathodesleeve 11 and a fiat rhomboidal shaped wrap 25 prior to labelling. Wrap25 is similar to Wrap 15 in FIG. 1 in that both may be made from thesame material and both may be applied by similar labelling processes.However, wrap 25 in FIG. 3 differs from wrap 15 in FIG. 1 in that wrap25 is of rhomboidal shape, i.e., it is cut to include two acute cornerangles 27 and two obtuse corner angles 29, while rectangular wrap 15 inFIG. 1 includes four corner angles.

FIG. 4 shows rhomboidal shaped wrap 25 of FIG. 3 after it has beenattached to cathode sleeve 11 by any one of the previously mentionedlabelling processes. It will be noted that wrap seam 31, in FIG. 4, isspiral in form and that the spiral seam 31 makes approximately onecomplete turn around the cathode from top to bottom. The rhomboidalshaped wrap of FIG. 4 with its one-turn spiral seam is the optimum shapefor minimizing possible loss in electron emission due to orientation ofthe surface discontinuity of seam 31 relative to the grid.

Referring now to FIG. 5, the cathode of FIG. 4 is shown in mountedposition Within a grid 33 comprising grid laterals 35 and a pair of siderods 37. In the particular cathode-grid arrangement shown in FIG. 5 themajor areas of high emission density on coating 25 are those areas mostclosely adjacent grid laterals 35, and it is in these areas that thevertical seam 17 of a FIG. 1 type cathode causes the greatestdifficulty. When rhomboidal shaped wrap 25 with its spiral seam 31 isused, however, it can be seen that the coating areas most closelyadjacent grid laterals 35 contain only a small portion of the wrappedseam 31 and that the major portion of wrap seam 31 is positioned in lesscritical areas in which lower emission densities are normally realized.Also in the structure of FIG. 5, rotational orientation of cathode 11relative to grid 33 makes little if any difference as far as emissioncharacteristics are concerned. In other words, cathode 11 with itsspiral seam wrap, as shown in FIG. 5, may be assembled on a tube mountby a machine incapable of orienting the cathode relative to the grid,without concern as to the final position of wrap seam 31 relative to thegrid laterals 35. Regardless of the rotational position of cathode 11there is always a given length of wrap seam 31 in the critical emissionareas and this length of wrap seam 31 changes little from tube to tube.Though it is true that in one tube the wrap seam 31 may appear at thetop and the bottom of the critical areas and in the next tube the wrapseam 31 may appear more closely centered in the electron window, in mosttube types the vertical position of the spiral seam 31 relative to thecritical cathode emission area has been found to be relativelyunimportant.

While the structure of FIG. has been shown with a spiral seam 31 of onecomplete turn, it is to be noted that a spiral seam 31 of less than oneturn also provides substantial advantages over the vertical seam priorart structure as shown in FIG. 1. Thus, in some tube types it may bedesirable to provide a rhomboidal shaped wrap with a seam ofapproximately a half turn or some other portion of a whole turn. Thoughthe cathode rotational orientation problems would not be completelyminimized with a cathode seam of less than a full turn, the shortenedspiral seam, if by chance it became positioned in a critical emissionarea upon assembly, would provide a critical area emission considerablyimproved over a cathode of the prior art vertical seam type where thevertical seam was positioned in a critical area.

The exact rhomboidal shape ultimately used in any given tube type mayprove to be a compromise between a solution to the critical areaemission problem and the problem of attaching the wrap to the cathode bya given labelling process. The cut cathode wrap, he it of a prior artrectangular shape or a rhomboidal shape, as taught herein, is of afragile nature, and it has been found that in some films it is difiicultto wrap a sharp cornered rhomboidal shape without excessive shrinkage orloss arising from either film breakage at a relatively sharp corner orpoor bonding between the sharp corners and the cathode sleeve. Thus, intube types where such fragile films are necessary, it may be desirableto cut a rhomboidal wrap which makes only a partial spiral seam andaccept the variation which arise in emission characteristics from tubeto tube in order to realize a wrap shape more easily attached to thecathode sleeve by usable labelling techniques.

Though the invention has been described in connection with a cylindricaltype cathode it is to be noted that cathode sleeves or bases of a shapeother than cylindrical may be wrapped as taught herein. For example,though sleeves of rectangular cross section are more easily preorientedthan cylindrical sleeves, it may be desirable when using a rectangularcross sectioned cathode sleeve to dispense with the orientation problemand use a spiral wrap as taught herein.

Cathode wraps cut to provide a spiral seam of more than one turn areunsatisfactory both from the labelling technique viewpoint and theemission viewpoint. As the spiral seam is lengthened over one turn, thelength of wrap seam in the critical area increases with a resulting lossof possible emission over the critical area. Further, even withoutconsidering emission characteristics it would be extremely diflicult toattach a wrap of more than one turn without extremely high shrinkage orrate of loss.

The use of a rhomboidal shaped wrap of one turn or less distributes thepossible loss in cathode emission from a gap seam over the surface areaof the cathode so as to minimize emission variations while at the sametime minimizing rotational orientation problems between the cathode andthe grid.

While there has been shown and described what is at present consideredthe preferred embodiment of the present invention, it will be obvious tothose skilled in the art that various changes and modifications may bemade therein without departing from the appended claims.

Having thus described my invention, I claim:

1. "In an electron tube cathode of the wrap-around coated type thecombination comprising a cathode base sleeve and an attached rhomboidalshaped coating sheet having opposite edges forming a spiral seam, saidspiral seam being no longer than one turn around the cathode basesleeve.

2. In an electron tube cathode of the wrap-around coating type thecombination comprising a cylindrical metal cathode base and an attachedrhomboidal shaped coating sheet having opposite edges forming a spiralseam, said spiral seam being no longer than one turn around the cathodebase.

3. In an electron tube cathode the combination comprising a cylindricalcathode base and a spiral wrapped rhomboidal shaped film of cathodecoating material, said spiral being no more than one turn.

4. In an electron tube cathode the combination comprising a metalcathode base supporting an attached spiral wrapped rhomboidal shapedfilm of cathode coating material, said spiral being no more than oneturn.

5. In an electron tube cathode the combination comprising a metalcathode base and an attached spiralseamed film of cathode coatingmaterial, said spiral seam being no longer than one turn around saidbase.

6. In an electron tube cathode the combination comprising a metalcathode base suitable for wrapping with a sheet of coating material, andan attached rhomboidal shaped sheet of coating material having opposededges forming a spiral seam of less than one turn around the cathodebase.

7. In an electron tube cathode the combination comprising a cathodecoating support base suitable for wrapping with a sheet of coatingmaterial, and an attached rhomboidal shaped sheet of coating materialhaving opposed edges forming a spiral seam of less than one turn aroundthe cathode base.

No references cited.

